Europol has warned that militants from so-called ISIS will aim to step up attacks on European targets, as they face defeat in the Middle East.
The European police force says more foreign fighters will try to come back to Europe, and "several dozen" capable of attacks could already be there.
It warns that some Syrian refugees in Europe may be vulnerable to recruitment by extremists who infiltrate refugee camps, BBC reports.
The report said the EU faced a range of threats and attacks from both organised networks and lone actors, either directed or inspired by IS and involving a range of weapons including bladed weapons and vehicles.
Home-made, commercial and military explosives in improvised devices such as those used in Syria and Iraq had not yet been used in Europe but this was "conceivable... at some stage", it added.
